The subject of the present invention is an improvement to delay igniter plugs for pyrotechnic machines, these machines being in particular grenades usable by hand or with mechanical launch means, and having explosive, smoke-generating, light-production or combined functions.
French Patent no. 76 00 800 describes an igniter plug provided with a trigger lever fitted with a locking pin and associated with a percussion mechanism for a sealed pyrotechnic module. The latter comprises an initiator, a delay composition, a primary explosive and a principal initiation charge capable of ensuring the initiation of the charge of the associated machine, this module being made integral in a leaktight manner with the body of the plug.
This plug has the advantage of guaranteeing sufficient leaktightness between the igniter system and the other constituent elements of the pyrotechnic chain of the module, so that the primary explosive cannot be initiated other than through the delay composition.
The first addition no. 76 17 248 to the aforementioned patent describes means for guiding the trigger lever in rotation over a given angular sector, after unlocking of this lever, so as to allow quasi-instantaneous release of the lever in question as soon as it has exceeded the guidance angular sector. According to a preferred embodiment, the body of the plug is also provided with two lateral slopes arranged beneath the trigger lever, so as to guide the latter in rotation after unlocking, and by interaction of the slopes with two corresponding lateral cheeks of the lever.
In these two known embodiments, the pyrotechnic module, which is mounted stationary with respect to the body of the plug, constitutes a complete pyrotechnic chain, capable of functioning in the case of accidental excitation of the primer, besides normal mechanical triggering by the lever and its associated percussion mechanism, this normal triggering comprising, in order, removal of the pin, release of the lever and percussion of the primer.
It has thus been observed that hand grenades can explode accidentally in the case of falling onto very hard ground, prolonged storage in premises with an abnormally high temperature, exposure to electromagnetic fields leading either to induced currents or to the formation of electrostatic charges which can influence, either by direct action, or by discharge, premature functioning of the primer.
In the aim of improving the safety of the storage and of the use of these pyrotechnic machines, in particular by removing any risk of accidental triggering of the principal primer charge and consequently of the charge of the corresponding machine, French Patent no. 78 17 119 described an igniter plug in which the pyrotechnic module is separated from the principal primer charge, and the igniter plug is fitted with a safety device capable of preventing triggering of the principal primer charge in the case in which the excitation of the primer has an origin other than the normal percussion mechanism of the plug.